An Army private accused of the largest leak of classified material in US history has pleaded guilty to reduced charges, saying he released the documents to "spark a domestic debate".

Private First Class Bradley Manning gave a detailed explanation of his actions in a military courtroom as he entered guilty pleas to 10 of the 22 charges against him.

Reading from a 35-page prepared statement, Manning said: "I believed that if the general public, especially the American public, had access to the information ... this could spark a domestic debate on the role of the military and our foreign policy in general."

The former intelligence analyst, who is accused of sending hundreds of thousands of classified documents to the whistle-blowing website WikiLeaks, added: "I felt I accomplished something that would allow me to have a clear conscience."

A military judge accepted Manning's guilty plea to the lesser charges of violating military regulations, which could carry a sentence of up to 20 years in prison.

Prosecutors say they plan to move forward with an additional 12, more serious, charges against him, including aiding the enemy - a charge that could carry a life sentence.

Manning, a 25-year-old Oklahoma native, admitted that he leaked Iraq and Afghanistan battlefield reports, State Department diplomatic cables, other classified records and two battlefield video clips in 2009 and 2010 while working in Baghdad.

The battlefield reports were the first documents that Manning decided to leak. He said he chose to send them to WikiLeaks after his efforts to give them to The Washington Post and The New York Times were rebuffed.

Image Caption:Manning supporters protest outside Fort Meade

Manning said that, in his experience, the battlefield reports were not treated as especially sensitive, particularly after the events they documented faded into the past.

He said he was concerned about leaking hundreds of thousands of sensitive State Department cables, but that he ultimately decided they would not be harmful since they were so widely distributed within the military.

"I thought these cables were a prime example of the need for a more open diplomacy," Manning said. "I believed that these cables would not damage the United States. However, I believed these cables would be embarrassing."

The Obama administration has said releasing the information threatened valuable military and diplomatic sources and strained America's relations with other governments.

Manning has been embraced by some left-leaning activists as a whistle-blowing hero whose actions exposed war crimes and helped trigger the Middle Eastern pro-democracy uprisings known as the Arab Spring in 2010.

WikiLeaks has been careful never to confirm nor deny whether Manning was the source of its cache of leaked US documents. The secret-spilling site did not deviate from that approach following Manning's testimony, continuing to refer to the Army private an "alleged source" on its Twitter feed.

But WikiLeaks has made no secret of its admiration for what Manning said was his decision to expose the documents to the world.